This painting of the inside of Cyfarthfa Ironworks at Merthyr Tydfil is an example of using a single perspective point or ‘vanishing point’. This is the point where the straight lines of the building point. The artist, Penry Williams, put his perspective point in the dark archway in the distance. If you follow the lines of the roof or the lines of the paving, you can see they all meet at this one place.
The roof has trusses that go from side to side and rafters that go away from the viewpoint. Because the artist was looking straight-on, he drew all the side-to-side lines as horizontal. You can imagine how these horizontal lines make triangles with the lines below them that go towards the perspective point. He drew columns exactly vertically.